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Thinking of interconnects between devices in Systems on Chips/Networks on Chips, what is a crossbar?

This term is used a lot (in contrast to a backpane bus - wiring that connects all components) in literature about these sort of devices and I wonder if someone here could provide a compact yet comprehensive definition - is it just a point to point connection?

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don't know but maybe similar to comparison between bus and star in the subject of network topologies. If so then each node is connected point to point to a central point, but not to each other. – barlop Jun 19 '12 at 15:07
up vote 3 down vote accepted

God, its been years since i've heard of this - i believe the old SGI octane i have lying around uses a crossbar switch, though its used elsewhere as well.

Its not quite point to point - its closer to connecting components as a grid, rather than a bus - this lets you connect any point on one 'axis' to another axis. This pretty much means any component on the grid can connect to any other component directly, but with less complexity than a true dedicated point to point connection.

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A full crossbar can connect any master to any slave on the bus, so has much more potential bandwidth if you have many parallel data-transfer tasks going on.

Compare with a multi-drop backplane bus like PCI where only one master can be transferring data at a time.

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